This invention relates to catheters.
The invention is more particularly concerned with balloon catheters, such as for use in angioplasty or balloon dilatation.
Balloon catheters are commonly used in angioplasty procedures to dilate blood vessels which have become occluded by sclerotic deposits. They comprise a hollow inner and outer shaft with an inflatable balloon located near the patient or distal end of the catheter. The catheter is inserted by sliding it along a guide wire extending through the inner shaft until the balloon of the catheter reaches the location of the occlusion. The balloon is then inflated via an inflation housing at the proximal, machine end of the catheter in order to effect the desired dilatation of the blood vessel. When the procedure is completed, the balloon is deflated and the catheter is removed from the body.
In some catheters, such as described in GB 2130093, the balloon forms a part of the outer shaft. Fluid to expand the balloon is supplied via an annular gap between the inner and outer shafts. In such an arrangement, expansion of the balloon will result in a shortening of the overall length of the outer shaft thereby resulting in a change in the relative lengths of inner and outer shafts. This change in relative length is accommodated in conventional catheters at their machine end by means of a helical spring which allows relative movement between the two shafts and urges the balloon to its unexpanded condition when fluid pressure is removed. A sliding seal within the inflation housing prevents loss of fluid.
This arrangement is relatively complex and expensive and any restriction in this relative movement can compromise the performance of the catheter.